An improved EMD method for noisy signal analysis in Time-Frequency domain
Mousa
Rezaee
دانشیار، دانشکده مهندسی مکانیک، دانشگاه تبریز
author
Ali
Banan Nojavani
دانشجوی کارشناسی ارشد مهندسی مکانیک، طراحی کاربردی، دانشکده مهندسی مکانیک، دانشگاه تبریز
author
Amin
Taraghi Oskooie
دانشجوی کارشناسی ارشد مهندسی مکانیک، طراحی کاربردی، دانشکده مهندسی مکانیک، دانشگاه تبریز
author
text
article
2014
per
Hilbert-Huang Transform is a new method for processing signals that applied to processing signals received from mechanical systems in recent years. This method for signals without noise leads to favorable results. However, in most cases the experimental signals are affected by the measurement noises which causes more complexity of signal processing and prevents extracting the correct information. In this paper, by applying some modifications to the Hilbert-Huang Transform, using the method for noisy signals has been provided. To this end, modifications have been done to the EMD method for signal decomposition. In the proposed method, instead of using Cubic Spline for the envelop curves, Smoothing Spline has been used. This modification causes to reduce noise effects and leads extracting better results from the experimental signal. Moreover, due to the complexity of experimental signals, sometimes stopping criterion used in common EMD method causes computational error and stops the program. By applying the modifications, the problem has been resolved as well. To study the efficiency of the proposed method, vibration response of a cracked beam in presence of and without noise was analyzed in the Time-Frequency domain by both conventional and the modified methods. Results indicated the superiority of the modified method in the presence of noise.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
16
v.
1
no.
2014
6
20
https://jmep.isme.ir/article_27238_d822bc03f0dda36bd491161b1788c06e.pdf
Nonlinear vibration analysis of a two-degree of freedom system at simultaneous resonance
Somaye
Ahmadsani
دانشجوی کارشناسی ارشد، دانشکده مهندسی مکانیک، دانشگاه صنعتی اصفهان
author
Hasan
Nahvi
دانشکده مهندسی مکانیک، دانشگاه صنعتی اصفهان
author
text
article
2014
per
To accurately predict vibration behavior of structures, a complete mathematical modeling is necessary. In nonlinear structural vibration analysis, using the linear model may lead to wrong results. In this paper, the nonlinear vibrations of a two-degree-of-freedom system consists of the main system and an absorber is studied at simultaneous secondary and internal resonances. The frequency response equations are obtained by solving the equations of motion using the method of multiple time scales (MTS). The effects of system parameters on the amplitude of the main system is investigated. Stability analysis is performed by the method of Andronov and Vitt and the saddle-node bifurcation points are detected. The results show that in the simultaneous super-harmonic and internal resonance case, system shows an almost linear behavior. Also, the nonlinear parameters of the absorber have insignificant effect on the amplitude of the main system. Unlike the linear case, when the nonlinear stiffness of the main system increases, the system amplitude increases as well. Finally, the domain of detuning parameter with three responses, resulted in the jump phenomenon in the response, is determined.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
16
v.
1
no.
2014
21
42
https://jmep.isme.ir/article_27239_2cdc3e29c53491dcca04feac98d0d689.pdf
Kinematic and dynamic performance of six-bar mechanism artificial knee
Narjes
Ghaemi
نویسنده مسئول، کارشناسی ارشد، دانشکده مکانیک، دانشگاه صنعتی نوشیروانی بابل
author
Morteza
Dardel
استادیار، دانشکده مهندسی مکانیک، دانشگاه صنعتی نوشیروانی بابل
author
Mohammasd Hasan
Ghasemi
استادیار، دانشکده مهندسی مکانیک، دانشگاه صنعتی نوشیروانی بابل
author
Hasan
Zohoor
استاد، دانشکده مهندسی مکانیک، دانشگاه صنعتی شریف
author
text
article
2014
per
Loss of limb has been a problem as long as man has been in existence. In order to restore the lost ability of amputees, artificial knee has been used by human. In this paper, the kinematic and dynamic performance of four types of six-bar mechanism used in the active knee prosthesis is investigated by computer simulation and discuss the differences criteria for four different classes of six-bar linkage mechanisms for fitting to amputees and compare improvement and weakening performance of the knees with together, and selected the best mechanism.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
16
v.
1
no.
2014
43
55
https://jmep.isme.ir/article_27240_0775f5cb1e795cf90dda58d546abb450.pdf
Inplane stress analysis of an isotropic strip containing several moving cracks
Rasool
Bagheri
دانشجوی دکتری، دانشکده فنی و مهندسی، دانشگاه زنجان
author
Mojtaba
Ayatolahi
نویسنده مسئول، دانشیار، دانشکده فنی و مهندسی، دانشگاه زنجان
author
Mehdi
Norozi
دانشجوی کارشناسی ارشد، دانشکده فنی و مهندسی، دانشگاه زنجان
author
text
article
2014
per
In this paper, analyses of several finite cracks with constant length (Yoffe-type crack) propagating in an isotropic strip were studied. The distributed dislocation technique is used to carry out stress analysis in an isotropic strip containing moving cracks under in-plane loading. The Galilean transformation is employed to express the wave equations in terms of coordinates that are attached to the moving crack. The solution of a moving edge dislocation is obtained in an isotropic strip by means of Fourier transform method. The stress components reveal the familiar Cauchy singularity at the location of dislocation. Finally several examples are solved and the numerical results for the stress intensity factor are obtained. The influences of the geometric parameters, the thickness of the isotropic strip, the crack size and speed have significant effects on the stress intensity factors of crack tips which are displayed graphically.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
16
v.
1
no.
2014
56
77
https://jmep.isme.ir/article_27241_30b53ae0695c5ad8f29b92f92babeae3.pdf
Investigation of the axial buckling and dynamic stability of functionally graded microshells based on the modified coupled stress theory
Raheb
Gholami
دانشجوی دکترا، دانشکده مهندسی مکانیک، دانشگاه گیلان
author
Abolfazl
Darvize
استاد، دانشکده مهندسی مکانیک، دانشگاه گیلان
author
Reza
Ansari
دانشیار، دانشکده مهندسی مکانیک، دانشگاه گیلان
author
Yoosef
Gholami
دانشجوی کارشناسی، دانشکده مهندسی مکانیک، دانشگاه گیلان
author
text
article
2014
per
Based on the modified couple stress theory, a size-dependent first-order shear deformation shell model is developed to investigate the axial buckling and dynamic stability of functionally graded microshells. The newly presented shell model capable of capturing the size effects. The higher-order governing equations and corresponding boundary conditions are obtained by using Hamilton’s principle. Afterward, using the Navier solution and Bolotin’s method, the axial buckling behavior and dynamic instability regions of simply-supported microshells are determined. A parametric study is presented to study the effects of various parameters such as the static load factor, dimensionless length scale parameter, material property gradient index, length-to-radius and length-to-thickness aspect ratios on the axial buckling and dynamic stability responses of microshells.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
16
v.
1
no.
2014
78
102
https://jmep.isme.ir/article_27242_3e903455c95bd975723c5091f904663b.pdf
-
text
article
2014
per
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
16
v.
1
no.
2014
6
19
https://jmep.isme.ir/article_44452_3d2db041b88a288e03508819a43ebd80.pdf